1. Field of the Invention
The present invention is concerned with the effective utilization of solar energy and, particularly, but not exclusively, with improvements in the type of solar energy collecting and distributing systems that circulate a gas (preferably air) rather than a liquid (usually water) to carry heat to storage or use. In that connection, it expands the merit of applicant's earlier application that matured into U.S. Pat. No. 4,029,081, granted June 14, 1977, and entitled "Solar Energy Transport System".
2. The Prior Art
Newkirk's "Flat Plate Solar Collector Handbook" and Mayall's "Applied Solar Energy" may be said to epitomize the art from which applicant's patent and the present invention have emerged. Thus, Newkirk says, inter alia:
"Flat plate solar collectors. . . are capable today of meeting the thermal energy needs for many types of systems such as domestic hot water heaters and building space heaters. This technology is considered to be immediately applicable for general us. . ."
The Mayall book gives much the same picture, and both set forth what have been considered disadvantages of a system that circulates air instead of water, i.e., that "more energy is required to move air than to move water", "duct work is relatively expensive and space consuming", and "the control system for air is more expensive than for water because the duct size is larger".
In any event, however, the first of these is overly optimistic, and a program recently sponsored by Northeast Utilities found performance of flat plate collectors far less than predicted because the prediction was based on pyrheliometer measurements of solar insolation, and the over-prediction was a consequence of inappropriate interpretation of the measurements.
To explain, only that radiation from the sun (insolation) can be properly counted which has an intensity and duration sufficient to bring the flat-plate absorber to a temperature--a source temperature--that is substantially above the use temperature--a sink temperature--to transfer energy. This is the general necessary condition for heat transfer. Thus, depending on the nature of use, when the sun is dimmed by atmospheric absorption, as at low solar altitudes; by haze or cirrus clouds, or by smog, so that the flat-plate temperature is not substantially above the intended use temperature--90.degree. C. (for storage in a sensible-heat storage facility); 65.degree. C. (for heating domestic water supply); 25.degree. C. (for heating living space); or the temperature of tap water (for pre-heating water for a conventional hot water system)--then the insolation must not be counted.